Just turned over 40,000 miles and was looking through the maintenance schedule, i replace the oil every 3000 miles and will inspect the filters. Other than that what is super important to check? I tow occasionally and drive on dirt roads also sometimes. Nothing is leaking and the truck feels like it is running great.

I plan on replacing the battery before the winter and doing the oil in 500 miles.

i think checking all the nuts and bolts you can reach and re torqueing, check your u joints, check hoses in the engine bay, 40,000 mi. really isn't alot of miles but regular maintenance like your doing is enough. greasing your zirks every oil change. I just hit 36,500 on my 2010. i just noticed your in alaska also, are you in anchorage?

Plugs every 30K on the v6. Not sure what's recommended for the trans, I have a manual. I changed trans, transfercase, front and rear diff oil at 42K when I bought the truck. I'm going to do those every 30K. It may not be needed with my relatively light use, but it's good insurance I think.

Other than that, check the brakes and anything else you can get to easily while you are under there.